The phosphorylation of protein on tyrosyl residues is now recognized to be an essential element in the control of such fundamental cellular processes as growth and proliferation, differentiation, cytoskeletal function and the cell cycle. We are currently witnessing an outstanding period of progress in characterizing the structure, regulation and function of both protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs), the coordinated action of which governs the levels of cellular phosphotyrosine. The objective of this meeting on "Reversible Tyrosine Phosphorylation and Cellular Signalling" is to provide a format in which the study of PTKs and PTP will be integrated to help participants see how their results contribute to the overall "big picture." We will organize the sessions based around physiological processes and cellular functions, rather than around particular categories of enzymes, so as to try and provide a biological context. With the exception of the Keynote Address by Tony Hunter, all speakers will be selected from submitted abstract. This will allow emphasis to be placed on encouraging graduate students, postdocs and young independent investigators to present the talks. It will also facilitate the presentation of the most recent and "hottest" results. We anticipate an attendance of 30-350 of which 64 will give oral presentations and approximately 160 will present posters. The funds requested in this proposal will enable more young investigators to participate, especially those who do not yet have independent funding. We hope that the integration of research on PTKs and PTPs at this meeting, placing emphasis on the biological roles of these enzymes, will engender a sense of cohesiveness and communication across the field.